基于m-序列的跳频序列集的构造与二维相关性分析

在雷达等高速移动的通信系统中,由于传输过程中的时延和多普勒频移,在分析跳频序列的性能时,需要对其时频2维汉明相关性进行分析。线性移位寄存器序列(m-序列)具有良好的随机、平衡等性质,因此m-序列已被广泛应用到跳频序列的构造中。该文对基于m-序列的跳频序列集的时频2维汉明相关性进行分析,计算了其时频2维汉明相关值的分布;构造了具有新参数的跳频序列集。在相同多普勒频移下,新序列集的2维相关性与已有基于m-序列的跳频序列集的2维相关性相比较更稳定。     

UHF频段卫星移动信道建模与仿真

分析了UHF频段卫星移动信道衰落特性,分析了4种典型场景下多径分量的多普勒功率谱和多径时延功率谱。利用WSSUS模型,结合电离层闪烁和阴影效应的程度,分别建立了4种场景下的信道模型。根据理论计算和参考文献分析了不同场景下信道的参数,对卫星移动信道模型进行了仿真,并给出了不同场景的误码率性能曲线。仿真结果表明,该信道模型能够真实反映UHF卫星移动信道的特性,对于卫星移动通信系统关键技术的研究具有指导意义。     

三维模型中的多普勒功率谱分析

多普勒效应是移动通信中最常见的现象,研究多普勒功率谱密度的分布,对建立更准确并贴合实际的无线信道模型具有重大意义。分析了两种不同几何模型中的多普勒功率谱,重点讨论了三维模型中入射波到达角度对多普勒功率谱的影响,仿真结果表明,方位角和高度角的分布及最大角取值范围共同决定了多普勒功率谱的分布特性。     

Wideband HAP-MIMO Channels: A 3-D Modeling and Simulation Approach

High-altitude platforms (HAPs) are considered as an alternative technology to provide future generation broadband wireless communications services. This paper proposes a three-dimensional (3-D) geometry-based reference model for wideband HAP multiple-input–multiple-output (MIMO) channels. The statistical properties of the channel are analytically studied in terms of the elevation angle of the platform, the antenna arrays configuration, and the angular, the Doppler and the delay spread. Specifically, the space-time-frequency correlation function (STFCF), the space-Doppler power spectrum, and the power space-delay spectrum are derived for a 3-D non-isotropic scattering environment. Finally, a sum-of-sinusoids statistical simulation model for wideband HAP-MIMO channels is proposed. The results show that the simulation model accurately and efficiently reproduces the STFCF of the reference model. The proposed models provide a convenient framework for the characterization, analysis, test, and design of wideband HAP-MIMO communications systems with line-of-sight and non-line-of-sight links.     

Representation of Laguerre-Gaussian modes by the Wignerdistribution function

The Wigner distribution function (WDF) of the general helical Laguerre-Gaussian modes are calculated in an analytical form. The propagation law of the WDF of the corresponding beams leads to the concept of generalized rays, 2-D subspaces of the 4-D phase-space are introduced in the form of sagittal and tangential planes. In these planes the WDF provides an intuitive picture of the focusing and twisting of the beam. The WDF's of the lowest helical mode in sagittal and tangential subspaces are depicted graphically in the phase-space and generalized ray representation, respectively. A global twist angle is introduced and discussed     

移动散射体下的V2V信道相关性和多普勒谱特性研究

该文首次提出两种典型的移动散射体存在的车辆对车辆(V2V)的无线传播信道模型,一种是基于一次散射发射(SBT)和一次散射接收(SBR)的信道,另一种是基于两次散射(DB)的信道,并在这两种模型的基础上给出了同时包含一次散射发射,一次散射接收,两次散射和视距(LOS)分量的信道模型。在假设移动散射体的运动速度和方向都随机且运动速度较小和较大的散射体速度分别用指数分布和混合高斯分布来描述的情况下,给出了这些传播信道的复增益,通过计算得到了信道的自相关函数(ACF)和多普勒功率谱密度(PSD)。文中还将理论计算得到的多普勒谱与已有文献的测量结果进行了对比,两者符合得较好。     

A Modified Loo Model with Partially Blocked and Three Dimensional Multipath Scattering: Analysis,Simulation and Validation

This paper presents a novel mobile fading channel model, belonging to the class of Loo models, in which the multipath power arrives both in three dimensions (3-D) and in two angular sectors at the azimuth receiver’s plane. Moreover shadowing affects the amplitude of the line of sight (LOS) component, making it time varying and following a lognormal distribution, as required for a Loo model. The Doppler power spectral density (PSD) is analytically calculated, after Fourier transforming the closed form autocorrelation function. Afterwards exact solutions for the probability density function (PDF) of the envelope and phase are presented. What follows are approximate solutions for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF’s). A new, appropriate for 3-D scattering cases, deterministic simulation scheme is developed, which implements the analytical model on a digital computer and is used to test the validity of the approximate solutions. Moreover the deterministic model is thoroughly investigated for all the possible cases, in terms of its convergence to the analytical one. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the modified Loo model.     

Analysis of a modified MIMO multi-bounced channel model for narrow street environment

To establish scattering models that match realistic street transmission scenarios for more efficient M2M mobile communication systems,existing models mainly focus on single-scattering and double-scattering,while for narrow urban street environment,single-scattering assumption is rather restrictive.To overcome this problem,a modified multi-bounced channel model based on EBSBM was provided,in which the concept of equivalent scattering point is assumed.The multi-bounced propagation paths are considered as an one-bounced ellipse scattering path and characteristics of the model were further analyzed.General formulations of several important parameters such as the probability density function (PDF) of the angle-of-departure(AOD),angle-of-arrival (AOA) and Doppler shift were derived,which were applied to the performance of multiple-input-multiple-output（MIMO）system employing a circular array antenna.Doppler frequency distribution was also taken into account.The results show good agreement with the previously models,which validates the rationality of proposed model.     

Stochastic fractal models for image processing

Our study of fractal landscapes departs from the simplest but yet effective model of fractional Brownian motion and explores its two-dimensional (2-D) extensions. We focus on the ability to introduce anisotropy in this model, and we are also interested in considering its discrete-space counterparts. We then move towards other multifractional and multifractal models providing more degrees of freedom for fitting complex 2-D fields. We note that many of the models and processing are implemented in FracLab, a software MATLAB/Scilab toolbox for fractal processing of signals and images.     

Time-frequency kernel design by the two-dimensional frequencytransformation method

A subclass of Cohen's class of time-frequency (TF) distributions is introduced in which the TF distribution kernels are provided via the frequency transformation method (FTM), used in two dimensional (2-D) filter design. The FTM kernels have finite extent in time and frequency and allow the TF distribution to be efficiently implemented in all four domains     

Sequence MAP decoding of trellis codes for Gaussian and Rayleighchannels

This paper considers the use of sequence maximum a posteriori (MAP) decoding of trellis codes. A MAP receiver can exploit any “residual redundancy” that may exist in the channel encoded signal in the form of memory and/or a nonuniform distribution, thereby providing enhanced performance over very noisy channels, relative to maximum likelihood (ML) decoding. The paper begins with a first-order two-state Markov model for the channel encoder input. A variety of different systems with different source parameters, different modulation schemes, and different encoder complexities are simulated. Sequence MAP decoding is shown to substantially improve performance under very noisy channel conditions for systems with low-to-moderate redundancy, with relative gain increasing as the rate increases. As a result, coding schemes with multidimensional constellations are shown to have higher MAP gains than comparable schemes with two-dimensional (2-D) constellations. The second part of the paper considers trellis encoding of the code-excited linear predictive (CELP) speech coder's line spectral parameters (LSPs) with four-dimensional (4-D) QPSK modulation. Two source LSP models are used. One assumes only intraframe correlation of LSPs while the second one models both intraframe and interframe correlation. MAP decoding gains (over ML decoding) as much as 4 dB are achieved. Also, a comparison between the conventionally designed codes and an I-Q QPSK scheme shows that the I-Q scheme achieves better performance even though the first (sampler) LSP model is used     

Large‐scale fading behavior for a cellular network with uniform spatial distribution

Large‐scale fading (LSF) between interacting nodes is a fundamental element in radio communications, responsible for weakening the propagation, and thus worsening the service quality. Given the importance of channel‐losses in general, and the inevitability of random spatial geometry in real‐life wireless networks, it was then natural to merge these two paradigms together in order to obtain an improved stochastical model for the LSF indicator. Therefore, in exact closed‐form notation, we generically derived the LSF distribution between a prepositioned reference base‐station and an arbitrary node for a multi‐cellular random network model. In fact, we provided an explicit and definitive formulation that considered at once: the lattice profile, the users' random geometry, the effect of the far‐field phenomenon, the path‐loss behavior, and the stochastic impact of channel scatters. The veracity and accuracy of the theoretical analysis were also confirmed through Monte Carlo simulations.     

Doppler spectrum in mobile-to-mobile communications in the presenceof three-dimensional multipath scattering

This paper provides analytical expressions for the time-autocorrelation function and the Doppler spectrum in a mobile radio channel in the presence of three-dimensional (3-D) multipath scattering. Mathematical modeling of the transmission channel is based on the assumption of wide-sense stationary (WSS) scattering. This paper deals with the case of a mobile-to-mobile radio link and derives formulas for the mobile-to-radiobase link as a special case. The Doppler spectrum examples provided are typical when assuming mobile terminal(s) located in densely built-up urban areas and simple dipole terminal antenna(s). Furthermore, the Doppler spectrum for transmission between a nongeostationary satellite and a mobile terminal located on the ground is analyzed. If different antenna patterns are to be considered and detailed knowledge is available on the multipath distribution, realistic Doppler spectra may be calculated using the approach presented in this paper     

版图设计对多指AlGaN/GaN HEMTs 栅指温度影响的研究

本文利用三维热仿真方法研究了不同版图设计对多指AlGaN/GaN 高电子迁移率器件工作温度的影响。我们使用拉曼微区测温技术测量了样品的沟道温度,并用于确定材料的热导率,验证器件热模型的准确性。建立模型时特别考虑了界面热阻的作用,确保器件温度分布的仿真结果与实验测量结果一致。文中采用包含界面热阻效应的三维热模型,系统的分析了栅指数目,器件栅宽和栅栅间距等因素对AlGaN/GaN 高电子迁移率晶体管热特性的影响。最后,提出了一种优化器件栅指间距的热设计方法,能够有效降低器件工作时的最高温度。     

考虑量子效应的短沟道n-MOSFET表面电势分布数值模型

提出了一种考虑量子效应的短沟道沟道表面电势数值模型,并在此基础上分析了源漏偏压对表面势分布的影响.计算结果和二维量子力学数值模拟结果很好地吻合.结果表明：源漏偏压会造成线性区的沟道表面势减小,进而导致阈值电压下跌;而在饱和区,源漏偏压的影响更大,会造成表面势明显下降,阈值下跌将会更加严重.     

A novel 3-D scattering model of 1.8-GHz radio propagation inmicrocellular urban environment

This work presents a novel three-dimensional (3-D) scattering model to predict the path loss of a microcellular radio channel in an urban environment. The analytical scattering model combined with a patched-wall model predicts the median path loss more accurately than the conventional analytical ray-tracing model in the cases studied. Comparing the path loss with the measured one at 1.8 GHz demonstrates the effectiveness of the scattering model. The scattering model includes three major propagation modes: (1) a direct-path wave; (2) a ground-reflected wave; and (3) the scattered field from the walls aligned along a street. The proposed model with a polarization scattering matrix associated with the patched-wall model aptly describes the third mode, which is usually neglected or oversimplified     

The relationship between Oxide charge and device degradation: A comparative study of n- and p- channel MOSFET's

We present a comparative study of device degradation for conventional n- and p-channel MOSFET's. The experimentally determined features of degradation are investigated with a 2-D simulation including fast and slow interface states as well as channel mobility degradation due to Coulomb scattering off these charges. Three different models concerning kind and spatial distribution are studied. We present a model that self-consistently describes the observed experimental features in the pentode and subthreshold regimes of the device. Furthermore, the substrate current is included in this analysis.     

A computer model for the simulation of thin-film silicon-hydrogenalloy solar cells

A 1-D computer simulation code, Thin-Film Semiconductor Simulation Program (TFSSP), for the modeling of TF Si:H solar cells is discussed. The code incorporates a variety of physical models, such as a position-dependent bandgap, electron affinity, dielectric constant, density of states, mobility, exponential band tails, and dangling-bond defect states. This flexibility allows different model assumptions to be analyzed and compared. TFSSP and the physical models used are described. An example simulation of a typical TF Si:H solar cell is presented     

Generic Carrier-Based Core Model for Undoped Four-Terminal Double-Gate MOSFETs Valid for Symmetric, Asymmetric, and Independent-Gate-Operation Modes

A generic carrier-based core model for undoped four-terminal double-gate (DG) MOSFETs has been developed and is presented in this paper. The model is valid for symmetric, asymmetric, and independent-gate-operation modes. Based on the exact solution of the 1-D Poisson's equation in a general DG MOSFET configuration, a rigorous derivation of the drain-current equations from the Pao-Sah's double integral has been performed. By using the channel carriers as the intermediate variable, a very compact analytical drain-current expression can be obtained. The model is extensively verified by comparisons with a 2-D numerical simulator under a large number of biasing conditions. The concise mathematical formulation allows the unification of various DG models into a carrier-based core model for a compact DG MOSFET model development.     

Angle and Time of Arrival Statistics for a 3-D Pie-Cellular-Cut Scattering Channel Model

In this paper, investigated a 3-D pie-cellular-cut (PCC) scattering channel model for microcell environments, that idealizes the mobile station (MS) located inside of a 3-D scattering semispheroid and base station (BS) employing a directional antenna at the center of the semispheroid. The joint probability density functions (PDFs) and marginal PDFs of Angle of arrival (AOA) and Time of Arrival (TOA) seen at the BS and the MS in correspondence with azimuth and elevation angles are derived. The results show that the proposed 3D scattering channel model performs better compared with previously proposed 2D models for outdoor and indoor environments, which promotes the research of the statistical channel models.